1. Field of the Invention
The present invention relates to a magnetic disk apparatus used in a computer system and, more specifically, the present invention relates to a magnetic disk apparatus including a plurality of magnetic disks and a magnetic head assembly with improved floating sliders having magnetic heads secured thereto and carried by head arms moving radially over the magnetic disks to access to the magnetic disks for reading and writing data.
2. Description of the Related Art
A magnetic disk apparatus comprises a plurality of coaxially arranged magnetic disks and a magnetic head assembly including a rotatable or swingable head carriage which comprises a hub and a plurality of head arms extending from the hub in a line. Each of the head arms carries two floating sliders each of which secures one or two magnetic heads for reading and writing data on the magnetic disks. The floating slider has a pair of parallel rails on the surface thereof facing the associated surface of the magnetic disk to act as an air bearing while the magnetic disk is rotating, so that the floating slider flies above the surface of the magnetic disk by a certain distance against an elastic bias applied to the floating slider.
Floating sliders are disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) No. 3-283150, No. 61-246974, No. 62-42374, No. 4-271074, No. 4-57260, and 3-230379.
One of the problems of floating sliders is that there is a variation in the flying height of the floating slider above the surface of the magnetic disk while the magnetic disk is rotating and the floating slider moves from the innermost track to the outermost track of the magnetic disk or vice versa. The flying height of the floating slider above the magnetic disk is a function of an amount of air which is dragged, by the motion of the disk, between the slider and the rotating magnetic disk. If the magnetic disk is rotating at a constant rate, the speed of the surface of the magnetic disk varies depending on the radial position of the surface. The amount of the wind which the floating slider receives varies according to which track (radial position) of the magnetic disk the floating slider is positioned on. Thus the floating slider is closer to the magnetic disk when the floating slider is positioned on a radially inner track of the magnetic disk and the floating slider is further from the disk when it is positioned on a radially outer track.
In addition, the flying height of the floating slider above the magnetic disk varies depending on the angle that the rails of the floating slider form with the tangent line to the track of the magnetic disk over which the floating slider is positioned. Conventionally, the magnetic disk apparatus is designed such that the rails are parallel to the longitudinal axis of the floating slider, and when the floating slider is positioned on an intermediate track the angle the rails on the floating slider form with the tangent to the radially intermediate track is zero. The floating slider is thus able to fully accept the air flow caused by the rotating magnetic disk when the floating slider is positioned on the intermediate track. If the floating slider is positioned either on the radially inner or outer track, the angle the rails of the floating slider form with the tangent line of that track is not zero but a certain value, and the floating slider receives the wind from an oblique angle, resulting in a reduction of the flying height of the floating slider.
Accordingly, the flying height of the floating slider above the magnetic disk is small when the floating slider is positioned on the radially inner track due to the low peripheral speed and the angle between the floating slider and the tangent line on the radially inner track, and the flying height of the floating slider above the magnetic disk is large when the floating slider is positioned on the radially outer track which has a high peripheral speed. Accordingly, the variation in the flying height of the floating slider above the magnetic disk depends on whether the floating slider is positioned on the radially inner track or on the radially outer track. For example, the difference in the flying heights in the conventional design may be 0.06 to 0.08 microns.
This difference in the flying height becomes a problem in recent magnetic disk apparatuses, in particular, in apparatuses which use a zone bit recording system in which the data transfer speed is varied depending on the radial position of the magnetic disk to keep the recording density uniform throughout the magnetic disk, irrespective of the position of the magnetic head.